Around 200 people were working at the Kleen Energy plant in Middletown, which is due to open this summer.

According to Middletown mayor Sebastian Giuliano search experts and specialist dog teams are at the site combing through the wreckage.

"How many people were here today - that's the number they can't really nail down. They were purging gas lines all night long, most people were evacuated from the building when they ran the tests," Giuliano said.